Electron-discharge apparatus



Jan. 14, 1930.. c. SPAETH ELECTRON DISCHARGE APPARATUS 2 Sheets-Sheet 1 Filed Jan. 18, 1-926 Jan. 14, 1930. c, SPAETH 1,743,629

ELECTRON DI SCHARGE APPARATUS Filed Jan. 18, 1926 2 Sheets-Sheet 2 K220672507" Car/s jm'efk Patented Jan. 14, 1930 UNITED STATES PATENT OFFICE" CHARLES SPAETH, OF CHICAGO, ILLINOIS, ASSIGNOR, BY MESNE ASSIGNMENTS, TO

OLD COLONY TRUST COMPANY, A CORPORATION OF MASSACHUSETTS, TRUSTEE ELECTRON-DISCHARGE APPARATUS Application filed January 18, 1926. Serial No. 82,019.

My invention relates to a thermionic vacuum tube with a filament energized by alternating current and to a radio receiving circuit employing such a tube.

It is a purpose of my invention to provide a thermionic vacuum tube or electron discharge tube for radio apparatus that is provided with a filament that may be energized by means of a current having periodic characteristics such as an alternating current without producing any objectionable hum or other noise in the sound reproducing apparatus associated therewith due to the frequency of the periodic characteristics of the current. The filament may, of course, be energized by unidirectional current if desired.

It is a purpose of my invention to provide means for establishing a neutral point on the filament of an electron discharge tube which is energized by alternating current and to provide a connection between the grid element and saidneutral point whereby the grid element is maintained at substantially a constant normal potential when the potential thereof is not being modulated by means of high frequency signals, thereby preventing the variation in the potential of the grid element ordinarily brought about due to the alternations of the current in the filament and avoiding the hum that would otherwise exist in a telephone receiver or other sound reproducing means connected or coupled with the output circuit of the electron discharge tube.

It is a further purpose of my invention to provide a new and improved radio receiving apparatus wherein such electron discharge tubes energized by alternating current are employed and to provide an arrangement in said apparatus whereby a neutral point is established on the filament and whereby a neutral point is provided correspondingto said point on the filament with which the grid element may be connected. In supplying the alternating current to the filament of the tube, a transformer is employed having a secondary winding provided with means connecting the opposite terminals of the winding with the terminals of the filament and which is further provided with a tap between said terminals that is connected with a neutral point, such as the ground. The filament is also provided with means for connecting a point between the ends thereof with a neutral point, such as the ground.

It is a further purpose of the invention to provide an electron discharge tube of the character set forth above with a filament that is provided with a tap substantially midway between the ends thereof that may be connected with a neutral point, such as the ground, and to provide a pair of reactances that areeonnected respectively between the terminals of the filament and said tap and which are so proportioned relative to the reactance-of the portions of the secondary on opposite sides of the tap thereon that a balanced condition exists that is somewhat similar to that existing in a Wheatstone bridge.

Preferably, the two reactances are equal and are connected between the opposite ends of the filament respectively and a tap, that is arranged centrally of the filament. The reactances of the two portions of the secondary winding of the transformer are also preferably equal and must then" be equal to the reactances of the two windings connected between the tap and the terminals of the filament. The reactance of the portion of the secondary winding that is connected with one end of the filament must be equal to the reactance of the winding connected between said end of the filament and the tap leading from the filament, while the reactance of the other portion of the secondary winding must be equal to the other 'reactance connected be tween the other terminal of the filament and the central tap. When this condition exists, a condition of balance has been established similar to that in a Wheatstone bridge and by connecting the grid element of the tube with a neutral point that is thus established, the normal potential of the gridelement can be maintained substantially uniform when unmodulated by high frequency signals and can be prevented rom fluctuating in synchronism with the alternations of the current from the alternating current source.

the same absolutely accurate, it has been found desirable to provide means for adj usting the apparatus so that any such variations can be compensated for and the neutral point to which the grid element is to be connected established in spite of such inaccuracies in manufacture. It is a purpose of my invention to provide means for adj usting for such inaccuries to find the neutral point comprising an adjustable contact engaging with one of said reactances so as to connect the grid element at any point along the same where a neutral condition is found to exist.

It is another purpose of my invention to provide means for preventing the buildin up of a charge on the grid element which mlght otherwise take place due to the interposition of the reactance which acts to a certain extent similar to a choke coil between the grid element and the ground by providing a high resistance connected between said grid element and the central tap on the filament.

It is a further purpose of the invention to provide means for preventing the burning out of the filament by interpositioning a high resistance between the central point thereof at which the tap is made and the ground.

It is also a purpose of my invention to mount said high resistances which are preferably carbon rods, so that moisture will not effeet the same, this being accomplished by mounting said resistances within the vacuum tube in which the elements of the electron discharge device are mounted.

Other objects and advantages of the invention will appear as the description of the accompanying drawings proceeds. However, I desire to have it distinctly understood that I do not intend to limit myself to the exact details shown or described, but that I intend to include as part of my invention all such obvious changes and modifications of parts as would occur to a person skilled in the art and as would fall within the scope of the claims.

In the drawings:

Fig. 1 is a diagrammatic view of a radio receiving apparatus embodying my improved electron discharge tube energized by alternating current and the circuit connections used in conjunction therewith;

Fig. 2 is a side elevation partly broken away of an electron discharge tube embodying my invention, the reactances associated therewith being shown diagrammatically;

Fig. 3 is a similar view of such a tube embodying a plurality of plate elements and a plurality of grid elements.

Referring in detail to the drawings, in Fig. 1 is shown a radio receiving aparatus which may be of any standard type except for the features that particularly relate to my invention, but which is shown in the drawing as comprising one stage of radio frequency amlification, a rectifier and one stage of audio requency amplification. In Fig. 1 the antenna is indicated by the numeral 10 which is connected with the ground 11 through the variable condenser 12 and the primary winding 13. Con led with .the primary winding 13 is a secon ary winding 14 across the terminals of which is connected 9. variable condenser 15 for tuning the same. A fixed condenser 16 may be connected between the terminals of the windings 13 andl4.

One terminal of the winding 14 is connected with the grid element 17 of an electron discharge tube 18 which is made in accordance with my invention and which has a plate element 19 from which the conductor 20 leads to the primary winding 21 of a transformer having a secondary winding 22. The other terminal of the winding 21 is connected by means of the conductor 23 with the positive B battery terminal as indicated at the right of Fig. 1.

The filament of the vacuum tube 18 comprises the preferably substantially identical and equal portions 24 and 25. The portions 24 and 25 may be continuous or may be two separate filaments if desired, but in either event a tap 26 is provided substantially midway between the terminals 27 and 28 of the portions 24 and 25 or at the point of junction of the portions 24 and 25. Thus, a filament is provided that has terminals at the opposite ends thereof and that has a tap substantially midway between the ends thereof. The filament comprising the portions 24 and 25 is energized from a source of alternating current from which the conductors 29 and 30 lead which are connected with the terminals of the primary 31 of a transformer having a core 32 and a secondary winding that is provided with a tap 33, thus providing the portions 34 and 35 of said secondary winding on opposite sides of said tap 33. The opposite ends of the secondary winding are connected by means of the conductors 36 and 37 with the terminals 28 and 27, respectively, of the filament. The tap 33 leads to the ground at 38. A very high resistance 39 whichis preferably of one megohm or higher, is connected between the tap 26 and the conductor 40 leading to the ground at 41. The reactances 42 and 43 are lnterposed between the terminals 27 and 28 and the tap 26, being shown in the diagram as being mounted between the conductors 37 and 40, 40 and 36, respectively, said reactances preferably comprising inductively wound coils of resistance wire. A resistance 44 corresponding in value substantially to the resistanc 39 is interposed between the grid element 17 and the filament of the tube substantially at the tap 26, while a conductor 45 leads from the terminal of the secondary 14 opposite that to which the grid 17 is connected to the adjustable contact 46 which is adapted to engage at any point along the reactance 42.

The reactance of the portions 34 and 35 of the secondary and the reactance of the windings-42 and 43 are preferably all equal, the important feature being that the reactance of the portion 35 is equal to the reactance of the winding 42 and that the reactance of the portion 34 is equal to the reactance of the winding 43. The filament portions 24 and 25 being substantially equal in reactance, particularly where the type of vacuum tube is employed that is shown in Figs. 2 or 3, the result will be that due to the connection of the tap 26 and the tap 33 with the ground, a

balanced condition will exist providing a neutral point substantially Where the reactances 42 and 43 are connected together. This would be theoretically true if absolute accuracy of the positioning of the taps 33 and 26 could be obtained, but as this is not possible in commercial practice, it is necessary to provide the movable contact 46 whereby a point on the reactance 42 can be found that is neutral. When this neutral point is found, the potential of the grid 17 will be maintained constant when not modulated by high frequency signal impulses and there will be no hum produced in the output circuit of the tube 18. The high resistance 44 is provided so that a leakage exists from the grid to the neutral point in the circuit so as to prevent the accumulation of a charge on the grid 17 due to the high frequency currents.

One terminal of the secondary 22 is connected with any form of rectifier 47 which may be a detector tube or any other rectifying means. The other end of the secondary winding 22 is connected with an oppositely arranged rectifying means 47 and is further connected through the conductor 48 with the conductor 49 which leads to the negative terminal of the B battery and which is connected also with the ground 41 through the conductor 40. An audio frequency transformer having the primary 50, the secondary 51 and the core 52 is also provided, one terminal. thereof being connected with the rectifier 47 and the other with the rectifier 47 A condenser 53 is bridged across the terminals of the primary 50.

One terminal of the secondary 51 is connected with the grid 17 of the electron discharge tube 18' which is provided with a plate element 19 and witha filament having the portions 24' and 25'- which correspond to the portions 24 and 25 of the filament of the tube 18. said tubes 18 and 18 being made substantially alike'and being both energizable from an alternating current source in a similar iifanner. A high resistance 44 is also provided between the tap 26' on the filament and the grid 17. and the terminals27 and 28 of said filament are connected through the conductors 53 and 54 with the conductors 36 and 37, respectively, while the conductor 55 leadingfrom the tap 26 through the high- .are the reactances 34 and 35 and structed in a forms being *cal plate element 119, a coiled resistance 39' corresponding to the resistance 39 associated with the tube 18 is connected with the conductor 49 which is connected with the ground at 41. The reactances 42 and 43 correspond to the reactances 42 and 43 associated with the tube 18 and the conductor 45 which leads from the grid 17 through the secondary 51 and the C battery 56 is connected in a similar manner with the reactance 42 to that in which the conductor 45 is connected with the reactance 42 by any adjustable connection 46 which corresponds to the contact means 46 associated with the reactance 42. In the operation of the tube 18, a similar relationship of the reactances mustexist'as in the operation of the tube 18. Preferably, the reactances 42 and 43 are equal as preferably, said last mentioned reactances are also each equal to the reactances 42' and 43.

In order to obtain the balanced condition that is necessary,the reactance of the portion 34 of the secondary must be equal to the reactance of the winding 42. and the reactance of the portion 35 of the transformer must be equal to the reactance of the winding 43. The arrangement and operation of the devices associated with the tube 18 are substantially the same as those associated with the tube 18 except for the provision of the C battery 56, which is provided to place a strong negative bias on the grid 17'. As explained in connection with the tube 18, it is impossible to make the reactances in practice exactly the same and to place the tap 33 exactly in the middle of the secondary of the transformer.

, Accordingly, the neutral point must be found againby means of the adjustable contact 46 in a similar manner as it is found by means of the adjustable contact 46 for-the tube 18. Any suitable sound reproducing means is provided, such as a loud speaker or telephone receiver indicated by the numeral 57, which is connected through the conductor 58 with the plate element 19 and through the conductor 59 with the positive B battery lead 23.

.My improved vacuum tube may be conplurality of different ways, two shown in Figs. 2 and 3, respectively, and in Fig. 2 a glass vessel 118 is shown in which is mounted a substantially cylindrigrid element 117 that is substantially coaxial therewith and' a filament 120 which is mounted sub stantially on the center line of the grid 117 and plate 119, said filament being supported by means of a suitable supporting rod 121 which is provided with an end portion 122 extending over the plate element and which is mounted in the glass stem portion 123. The filament 120 is divided into two equal parts 124 and 125 by providing a tap 126 midway between the ends thereof. The tap 126 preferably extends through an opening 127 in the plate element 119, and is made of in Fig. 1, is preferabl vided in the outer end of the glass vessel 118 adjacent the tip 133 thereof, a supporting member 134 being anchored in said bead and extending downwardly therefrom and carryin the grid 117. The conductors 135 and 136 lead from the plate and grid elements, respectively, through the base of the tube in the usual magner, any suitable terminals being provided on the'base of the tube to make contact with any desired form of socket member. The conductors 137 and 138 lead from the opposite ends of the filament, as will be clear from Fig. 2, and a conductor 140 leads from the support 128 and thus from the tap 126. A high resistance 139 which is preferably of the value of the resistance 39 shown connected with the conductor 140 so as to e interposed between the tap 126 and the ground 141. The resistance 139 is preferably a carbon rod resistance and is preferably mounted within the chamber of the tube. The reactances 142 and 143 which correspond to the reactances 42 and 43 shown in Fig. 1 may be mounted in the base of the tube, if desired. A conductor 145 leads from the conductor 140 and from the opposite ends of the reactances 142 and 143, from those connected with the conductors 137 and 138, to the ground 141. The conductors 137 and 138 terminate in suitable terminals in the base of the tube in the usual manner. A high resistance 144 which corresponds to the resistance 44 in Fig. 1 is interposed between the support 134 and the tap 126, thus being interposed between the grid 117 and the tap 126. This is preferably a carbon rod resistance or one of similar material which is affected by moisture and is particularly advantageously mounted within the glass vessel 1-18 whereby any change in the resistance thereof due to moisture will not take place. An adjustable contact member 146 is provided on the winding 142 which corresponds to the adjustable contact 46 in Fi 1.

l n Fig. 3 another form of electron discharge tube embodying my invention is shown in which a plurality of plate and grid elements are provided. The glass vessel 218 has apair of grid elements 217 therein and a pair of plate elements 219, said plate elements and grid elements being arranged in concentric relation and each having a-filament mounted substantially on the axis thereof, said filaments being indicated by the numerals 224 and 225, respectively. Said filaments are supported by the supportin members 222 and 222' from which the conductors 237 and 238 extend in the stem portion 223 of the tube, the same extendin into the base indicated in dotted lines in Fig. 3 and terminating in suitable terminals. The upper ends of the filaments 224 and 225 are connected by means of the transversely extending supportingsmember 216 from which the tap 226 extends upwardly, said tap having a hi h resistance 239 connected therewith, sai high resistance 239 correspondin to the resistances 139 and 39 in Figs. 2 and 1, respectively. The resistance 239 and tap 226 are supported from the bead 232 and the conductor 240 extends from the tip of the tube 218 to the ground 241. The resistance 239 is preferably also a carbon rod and is particularly advantageously placed within the vessel 218 to prevent the same from being affected by moisture. The plate elements 219 are mounted upon the supporting members 229 and 230,.

the supporting member 230 connecting the two plate elements 219 together, as will be evident from Fig. 3 so that they act in efiect as one plate element. A transversely extending connecting member 215 is also provided between the grid elements 217 and this is preferably supported by means of any suitable support 214 at the upper end thereof, while the lower ends of the grid members 217 are supported in the stem portion 223 by means of the supports 231 and 231, the support 231 being provided with a conductor 236 extending throughthe base of the tube to any suitable terminal provided thereon. One of the supports 229 is also provided with a conductor through the stem and through the base member to any suitable terminal, said conductor being indicated by the numeral 235. A reactance 242 is provided between the conductors 237 and 238, thus mounting the same between the terminals of the filament, the whole filament being continuous from the bottom of the filament 224 through the connect ing portion 216 to the bottom of the filament 225. The terminals of the filament are connected with the terminals of the secondary v of the transformer in the manner shown in Fig. 1 and the conductor 240 corresponds to the conductors 40 in Fig. 1, thus providing the neutral point on the filament. The reactance 242 is provided with an adjustable contact member 246 whereby the neutral point on said reactance can be found, said ad ustable contact 246 corresponding to the contact 46 in Fig. 1. In this case the reactance 242 must be the sum of the reactances of the windings 34 and 35 in order to obtain the desired effect on the grid elements 217 and are connected with the adjustable member 246 in the manner shown in Fig. 1.

While various structural arrangements of the electron discharge tube may be provided to obtain the desired result, the preferred arrangement is such that the elements are ar ranged symmetrically such as shown in Figs.

2 and 3 with the plate element, grid element 5 and filament all arranged on the same axis, thus the capacity eifect along the length of the filament is the same and does not vary because of different spacing of the parts. This makes it possible to more readily balance the circuit so as to avoid the alternating current hum as described in connection with Fig. 1. The high resistance between the grid and tap on the filament and between the tap and the ground are preferably mounted within the chamber of the vacuum tube to prevent the same from being afiected by moisture and the reactances associated with the tube are preferably mounted in the base thereof so as to simplify the installation of the same by the users thereof.

In order to avoid any inductive efiect on the receiving circuit due to the presence of the conductors 36 and 37 through which alter nating current is flowing, the metal shell or screen 65 is provided enclosing the rectifiers 47 and 47 and the transformers having the windings 21 and 22 and the windings 50 and 51. The metal casing 65 is grounded by means of the conductor 66 connecting with 30 the ground at 41 through conductor 40, or in any other desired manner.

' Having thus described my invention, what I desire'to claim and secure by United States Letters Patent is:

1. An electron discharge tube having a filament provided with end terminals and a tap between the ends thereof, a neutral terminal and a high resistance connecting said tap and neutral terminal, plate and grid elements and a high resistance interposed between said tap and said grid element, said resistance being mounted within said tube.

2. In a device of the character described, an electron discharge tube. having a filament thereof, means for connecting a oint on said filament substantially midway etween the ends thereof with a neutral point, a winding interposed between each of said terminals and said means, a transformer having the primary thereof connected with an alternating current supply and-having the terminals of the secondary thereof connected with the terminals of said filament and a tap substantially midway of said secondary connected with a neutral point, the reactance of each of said windings being equal to the reactance of that portion of the secondary of said transformer interposed between the tap on said secondary and said winding.

3. In a device of the character described, an electron discharge tube having a filament provided with terminals at opposed ends thereof, means for connecting a point on said 65 filament substantially midway between the provided with terminals at opposed ends ends thereof with a neutral point, a winding interposed between each of said terminals and said means, a transformer having the primary thereof connected with an alternating current supply and having the terminals of the secondary thereof connected with the terminals of said filament and a tap substantially midway of said secondary connected with a neutral point, the reactances of said windings and the portions of said secondary on opposite sides of said tap being substantially equal.

4. In a device of the character described, an electron discharge tube having a plate element, a grid element, a filament, said filament having a tap substantially midway thereof connected 'with a neutral point, a winding interposed between each end of said filament and said tap, means connecting said grid element with said neutral point comprising a contact member adjustable along one of said windings, a transformer having the primary thereof connected with an alternating current supply and the terminals of the secondary'thereof connected with the terminals of ,said filament and a tap substantially midway of said secondary connected with a neutral point, said windings and the por -tions of said secondary on opposite sides of said tap being of substantially equal reactance.

5. In a device of the character described, an electron dischargetube having a filament provided with terminals at opposed ends thereof, said filament being grounded substantially midway between the ends thereof, a high resistance interposed between said filament and the ground, a reactance interposed between each of said terminals and said means, a transformer, a pair of secondary terminals connected with the terminals of said filament and a tap on said transformer substantially midway between said secondary terminals connected with a neutral point.

In witness whereof, I hereunto subscribe my name this 4th day of January A. D., 1926.

CHARLES SPAETH. 

